The present invention relates to a chassis structure for a motor vehicle.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Solutions involving constructive, technological and material-based lightweight constructions gain increasingly importance to reduce weight of chassis structures for motor vehicles in order to decrease fuel consumption and weight. In particular lightweight materials such as aluminum play an important role to reduce the so-called unsprung masses in the chassis region. This trend is further accelerated by the demand for low-emission and exhaust-free vehicles having hybrid or electric drive which because of the need for electric components adds significant weight that must be compensated by reducing the weight of other components. To ensure high strength and stiffness properties of chassis structures that are subject to high stress, such as pivot bearings, suspension arms, guide arms, A-arms, etc., while still having smallest possible own weight, demand for chassis components that are forged of aluminum with yield strength Rp0.2 of above 300 MPa and elongation at rupture A5 of above 10% increasingly grows. In addition, the use of extruded profiles of light metal, in particular chassis structures like suspension arms produced from extruded profiles of aluminum, gain more and more importance in view of their potential for lightweight construction as a result of their less massive cross sectional configurations compared to forged parts.
Besides yield strength as design criterion, chassis structures are also designed with stiffness in mind to cope with defined buckling loads, in particular load situations and crash events. Stiffness is predominantly dependent on cross sectional design and the modulus of elasticity of the used material. The modulus of elasticity of aluminum is about 70,000 kN/mm2 and thus three times smaller than the modulus of elasticity of steel. This causes the unwanted situation that the cross section of stiffness-critical structural zones of forged parts must be made even bulkier in order to obtain the required stiffness, resulting in added mass and thus higher weight.
In view of the trend for more compact constructions of automobiles also in the area of the chassis, the limitation of available installation space does not allow any increase in the cross section of structures in order to realize the required values for stiffness-relevant moments of resistance of cross sections of the structures, e.g. by using open or closed profiles of greater diameter to meet lightweight conditions.
As the stiffness-relevant modulus of elasticity of lightweight materials like aluminum and also other materials can be influenced only to a very limited extent, other approaches involve the use of a composite of materials that have a higher modulus of elasticity. For example, steel attachments of various geometrical shape and thickness having a modulus of elasticity of about 210,000 kN/mm2 can be forged onto stiffness-relevant regions of forged aluminum parts. A problem associated with this approach is the susceptibility of galvanic corrosion in galvanic relevant contact zones between aluminum as base material and the steel attachment and the corrodibility of the steel surface itself. This is especially a problem when considering that forged aluminum parts cannot be coated with an additional corrosion protection for cost reasons.
It is also known to employ different types of composites, e.g. layered composites, particle composites or fiber composites, etc. for various applications. This involves a layering of different materials. Cost reasons normally prohibit the use of such technologies for compact structures subject to high stress. High manufacturing costs also prohibit the use of metal matrix composites (MMC) which have increased modulus of elasticity through incorporation of ceramic fibers in the aluminum matrix. Approaches based on the use of CRP (Carbon-fiber-Reinforced Plastic), as known from motor sport, are also not an option for application in the conventional automotive field in view of their high costs and fairly brittle and low-deformation fracture behavior.
As described above, extruded profiles of light metal gain increasingly importance in addition to forged chassis structures. When chassis components such as suspension arms of extruded profiles with closed or open cross sections are involved, similar or same shortcomings are encountered as those stated above. Chassis structures of extruded profiles have cross sections that must be dimensioned over their entire length to suit the stiffness-critical section, even though this section normally constitutes only a small portion of the overall length of the structure. Thus, the extruded profiles are manufactured with a cross sectional geometry whose entire length is dimensioned to cope with an expected maximum load. Excess material that does not contribute to the stiffness and strength behaviors of the chassis structure is normally stripped mechanically to reduce weight of the structures. This requires additional expensive measures for machining the chassis structures and also for recovery and use of produced light metal scrap.
As each vehicle model family, depending on motorization and other equipment options, normally requires weight-optimized chassis structures for different load groups, extruded profiles of light metal require different cross sections. As a result, individual load group modifications require separate constructions, incurring significant added costs for employing different extrusion and machining tools and adding to the complexity of logistics.
It would therefore be desirable and advantageous to provide an improved chassis structure for a motor vehicle to obviate prior art shortcomings.